Screening and sieving machines of the aforedescribed type are widely used for separating particulates by size, the smaller particle size passing through the screen while the larger particles are discharged from the surface of the screen.
The oscillatory movement is usually imparted to the working screen by a connecting rod coupling the crankshaft with the working frame or by forming the working frame with a surface which rides on an eccentric surface of the eccentric drive so that the "throw" or eccentricity of the movement generated by the motor is applied to the working frame.
In general, the motor is mounted at a fixed location or on a structure which is fixed with respect to the working frame and thus the reaction forces which are generated when throw is imparted to the working frame may be taken up by the base frame or foundation structure on which the motor is mounted or which carries the journals of the eccentric drive assembly. The stress thus applied to the foundation is multiplied by the fact that the masses which are displaced by the drive are accelerated and thus momentum forces contribute to the loading of the support structure.
The energy which may be absorbed by the motor support structure is thus a function of the product of the mass which must be displaced and its acceleration.
It is difficult, if not impossible, with conventional oscillating machine designs to minimize the application of such stress to the environment of the machine, i.e. the base frame and foundation, while increasing the efficiency of the transmission of energy to the working frame.
The problem is that even more significant for mobile screening machines or screening machines which require some kind of adjustment of the position of the machine parts during operation such repositioning may be required for adjustment purposes and, namely, cannot be done without bringing the machine to a standstill.
With mobile machines which do not have the most stable purchase of the ground, the problem of dealing with the reaction forces is even more pronounced.